Our purpose in this investigation is to ascertain how the pituitary vascular system, whose structure we have previously described, actually functions. We propose to study the direction of blood flow within the porcine pituitary employing microcine-photography following intracarotid injection of lissamine green. Our purpose is to demonstrate that the pattern of blood flow within the putuitary is circular. The occurrence of circular blood flow within the pituitary implies that adenohypophyseal and neurohypophyseal hormones are delivered to the median eminence where the neurohypophyseal capillary bed is specialized--apparently to deliver hormones to the pars distalis, to the hypothalamus, and to the brain via the ventricular system. Our previous anatomic studies have emphasized the role of the neurohypophyseal capillary bed in the exchange of humoral messages between the adenohypophysis and the brain. However, alterations in the rate of neurohypophyseal blood flow will alter the rate of delivery of hormones to their target sites. We propose to characterize some of the factors regulating neurohypophyseal blood flow employing the radioactive-labelled microsphere technique in adult sheep and the 14C-iodoantipyrine technique in adult rats. Our aims are fourfold: (1) to determine if neurohypophyseal blood flow changes with changes in PaCO2 and autoregulates as does flow in other neural capillary beds, (2) to determine if neurohypophyseal blood flow changes with alterations in neurohypophyseal and/or adenohypophyseal function, (3) to determine if regional alterations in neurohypophyseal function are associated with regional changes in neurohypophyseal blood flow, (4) to relate alterations in regional neurohypophyseal blood flow to regional 14C-glucose utilization in the neurohypophysis and hypothalamus. The proposed investigation will increase our understandiing of neural control of pituitary function and of short loop feedback, and the means by which the pituitary can secrete to the brain to modulate brain function.